DTMF signalling between mobile and server

ABSTRACT

In a method of processing an incoming sequence of one or more DTMF tones at a mobile device, the sequence is decoded to thereby identify any encoded message. Where the decoding does not identify a message, at least applying an error correction algorithm to the sequence to identify a message. Where the algorithm fails to correct the sequence, the sequence is compared to messages currently expected by the mobile device. If a message is not identified, a negative acknowledgement message may be sent. At a server, upon receipt of a negative acknowledgement message, it is determined if a message was sent to the mobile device in a previous pre-determined time window. If so, the message is re-sent. The server repeatedly sends certain messages to a mobile device until an acknowledgement message indicating receipt of the message by the mobile device is received.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 12/693,055filed Jan. 25, 2010, the contents of which are incorporated herein byreference.

FIELD

The present application relates to DTMF signaling between mobile devicesand a server.

BACKGROUND

Many cellular devices today are capable of processing both voice callsand internet/computer data. These devices are commonly referred to as“smartphones”. With the advent of Voice-over-IP (VoIP) technology, ithas become possible to deliver voice calls over IP networks or over acombination of IP networks and the public-switched telephone network(PSTN) rather than solely over the PSTN, as was conventional.

In some systems, voice call services are provided via connection betweenmobile devices to an enterprise server. These systems may include asuite of call setup features and in-call features, such as thoseaccessible to a PBX-connected desk phone. These features may beimplemented by way of a signaling protocol between the mobile devicesand the server. For example, a request to invoke a particular feature bya mobile device may be encoded into a signal transmitted by the mobiledevice to the server. Typically, signals transmitted between the mobiledevices and a server are transmitted over the data channel. However, thedata channel may sometimes be unavailable for various reasons.

Therefore, signals transmitted between the mobile devices and a servermay be transmitted over the voice channel in DTMF. However DTMF is not areliable and efficient data transmission mechanism in general, so thereis a need for improved signaling between mobile devices and the voicemobility server.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings which show example embodiments of the present application, andin which:

FIG. 1A shows, in block diagram form, an example system for managingenterprise-related mobile calls, including an enterprise communicationsplatform;

FIG. 1B show, in block diagram form, another view of the example systemof FIG. 1;

FIG. 2 shows, in block diagram form, further details of an embodiment ofthe enterprise communications platform;

FIG. 3 shows another embodiment of the enterprise communicationsplatform;

FIG. 4 shows yet another embodiment of the enterprise communicationsplatform;

FIG. 5 shows further details of the enterprise communications platformof FIG. 3;

FIG. 6A is a signaling diagram generally indicating howmobile-originated, mobile-initiated calls are processed by the networkof FIG. 5;

FIG. 6B is a signaling diagram generally indicating howmobile-originated, PBX-initiated, calls are processed by the network ofFIG. 5;

FIG. 7A is a signaling diagram generally indicating howmobile-terminated, mobile-initiated calls are processed by the networkof FIG. 5;

FIG. 7B is a signaling diagram generally indicating howmobile-terminated, PBX-initiated calls are processed by the network ofFIG. 5;

FIG. 8 is a table of exemplary call control or call processing messagessent by mobiles to a server over a voice channel in the enterprisecommunications platform;

FIG. 9 is a table of exemplary call control or call processing messagessent by a server in the enterprise communications platform to mobilesover a voice channel in the enterprise communications platform;

FIG. 10 is table of an exemplary acknowledge and an exemplary negativeacknowledgement message sent by mobiles to the server over a voicechannel in the enterprise communications platform;

FIG. 11 is a flow diagram depicting a message receipt operation of amobile over a voice channel in the enterprise communications platform;

FIG. 12 is a flow diagram depicting a message identification operation amobile, which message identification operation is a step of the messagereceipt operation shown in FIG. 11;

FIGS. 13A, 13B and 13C are flow diagrams depicting message sendingoperations of the server over a voice channel in the enterprisecommunications platform;

FIG. 14 is a signaling diagram generally indicating how a mobileacknowledges a message over a voice channel from the server in theenterprise communications platform; and

FIG. 15 is a signaling diagram generally indicating how a mobileindicates receipt of an unknown message to the server over a voicechannel in the enterprise communications platform.

Similar reference numerals may have been used in different figures todenote similar components.

DESCRIPTION OF EXAMPLE EMBODIMENTS

In one aspect, the present application provides a method of processingan incoming sequence of one or more DTMF tones at a mobilecommunications device. The method includes decoding the sequence toidentify any message encoded by the sequence; where the decoding doesnot identify a message encoded by a given incoming sequence, at leastapplying an error correction algorithm to the incoming sequence toidentify a message from the given incoming sequence. The method furtherincludes where the error correction algorithm fails to correct,comparing the given incoming sequence to messages currently expected bythe mobile communications device.

In another aspect, the present application provides a method at a serverof communicating with a mobile communications device. The methodincludes upon receipt of an indicator indicating receipt by the mobilecommunications device of an unrecognized message, determining if a firstmessage was sent to the mobile communications device in a previouspre-determined window of time; and re-sending the first message if thedetermining determines that the second message was sent to the mobilecommunications device in the previous pre-determined window of time.

In yet another aspect, the present application provides a method ofvoice call handling at a mobile communications device. The methodincludes receiving over a voice connection at least one received tone,where each of the at least one received tone comprises a dual tonemulti-frequency (“DTMF”) signal; decoding the at least one received toneto identify a message; and where the message is a call answered message,sending at least one reply tone, the at least one reply tone encoding anacknowledgement message.

In yet another aspect, the present application provides a method ofvoice call handling at a mobile communications device. The methodincludes receiving a signal from a server; extracting a sequence of DTMFtones from the received signal; and identifying a message mapped by thesequence, if the sequence maps uniquely to a message. The method furtherincludes where the sequence does not map to any message, applying anerror correction algorithm to the sequence to produce a correctedsequence, and identifying a message mapped by the corrected sequence.The mobile sends a “negative acknowledgement” message to the server ifno message is identified.

Mobile devices implementing, and computer readable media containinginstructions which when executed implement, the disclosed methods areprovided.

Other aspects of the present application will be apparent to those ofordinary skill in the art from a review of the following detaileddescription in conjunction with the drawings.

Embodiments of the present application are not limited to any particularoperating system, mobile device architecture, server architecture, orcomputer programming language.

The present application relates to the control and management ofcommunications. Although reference may be made to “calls” in thedescription of example embodiments below, it will be appreciated thatthe described systems and methods are applicable to session-basedcommunications in general and not limited to voice calls. It will alsobe appreciated that the systems and methods may not be limited tosessions and may be applicable to messaging-based communications in someembodiments.

Reference is now made to FIG. 1A, which shows, in block diagram form, anexample system, generally designated 10, for the control and managementof communications. The system 10 includes an enterprise or businesssystem 20, which in many embodiments includes a local area network(LAN). In the description below, the enterprise or business system 20may be referred to as an enterprise network 20. It will be appreciatedthat the enterprise network 20 may include more than one network and maybe located in multiple geographic areas in some embodiments.

The enterprise network 20 may be connected, often through a firewall 22,to a wide area network (WAN) 30, such as the Internet. The enterprisenetwork 20 may also be connected to a public switched telephone network(PSTN) 40 via direct inward dialing (DID) trunks or primary rateinterface (PRI) trunks.

The enterprise network 20 may also communicate with a public land mobilenetwork (PLMN) 50, which may also be referred to as a wireless wide areanetwork (WWAN) or, in some cases, a cellular network. The connectionwith the PLMN 50 may be made via a relay 26, as known in the art.

The enterprise network 20 may also provide a wireless local area network(WLAN) 32 a featuring wireless access points. Other WLANs 32 may existoutside the enterprise network 20. For example, WLAN 32 b may beconnected to WAN 30.

The system 10 may include a number of enterprise-associated mobiledevices 11 (only one shown). The mobile devices 11 may include devicesequipped for cellular communication through the PLMN 50, mobile devicesequipped for Wi-Fi communications over one of the WLANs 32, or dual-modedevices capable of both cellular and WLAN communications. WLANs 32 maybe configured in accordance with one of the IEEE 802.11 specifications.

It will be understood that the mobile devices 11 include one or moreradio transceivers and associated processing hardware and software toenable wireless communications with the PLMN 50 and/or one of the WLANs32. In various embodiments, the PLMN 50 and mobile devices 11 may beconfigured to operate in compliance with any one or more of a number ofwireless protocols, including GSM, GPRS, CDMA, EDGE, UMTS, EvDO, HSPA,3GPP, or a variety of others. It will be appreciated that the mobiledevice 11 may roam within the PLMN 50 and across PLMNs, in known manner,as the user moves. In some instances, the dual-mode mobile devices 11and/or the enterprise network 20 are configured to facilitate roamingbetween the PLMN 50 and a WLAN 32, and are thus capable of seamlesslytransferring sessions (such as voice calls) from a connection with thecellular interface of the dual-mode device 11 to the WLAN 32 interfaceof the dual-mode device 11, and vice versa.

The enterprise network 20 typically includes a number of networkedservers, computers, and other devices. For example, the enterprisenetwork 20 may connect one or more desktop or laptop computers 15 (oneshown). The connection may be wired or wireless in some embodiments. Theenterprise network 20 may also connect to one or more digital telephonesets 17 (one shown).

The enterprise network 20 may include one or more mail servers, such asmail server 24, for coordinating the transmission, storage, and receiptof electronic messages for client devices operating within theenterprise network 20. Typical mail servers include the MicrosoftExchange Server™ and the IBM Lotus Domino™ server. Each user within theenterprise typically has at least one user account within the enterprisenetwork 20. Associated with each user account is message addressinformation, such as an e-mail address. Messages addressed to a usermessage address are stored on the enterprise network 20 in the mailserver 24. The messages may be retrieved by the user using a messagingapplication, such as an e-mail client application. The messagingapplication may be operating on a user's computer 15 connected to theenterprise network 20 within the enterprise. In some embodiments, theuser may be permitted to access stored messages using a remote computer,for example at another location via the WAN 30 using a VPN connection.Using the messaging application, the user may also compose and sendmessages addressed to others, within or outside the enterprise network20. The messaging application causes the mail server 24 to send acomposed message to the addressee, often via the WAN 30.

The relay 26 serves to route messages received over the PLMN 50 from themobile device 11 to the corresponding enterprise network 20. The relay26 also pushes messages from the enterprise network 20 to the mobiledevice 11 via the PLMN 50.

The enterprise network 20 also includes an enterprise server 12.Together with the relay 26, the enterprise server 12 functions toredirect or relay incoming e-mail messages addressed to a user's e-mailaddress within the enterprise network 20 to the user's mobile device 11and to relay incoming e-mail messages composed and sent via the mobiledevice 11 out to the intended recipients within the WAN 30 or elsewhere.The enterprise server 12 and relay 26 together facilitate “push” e-mailservice for the mobile device 11 enabling the user to send and receivee-mail messages using the mobile device 11 as though the user wereconnected to an e-mail client within the enterprise network 20 using theuser's enterprise-related e-mail address, for example on computer 15.

As is typical in many enterprises, the enterprise network 20 includes aPrivate Branch eXchange (although in various embodiments the PBX may bea standard PBX or an IP-PBX, for simplicity the description below usesthe term PBX to refer to both) 16 having a connection with the PSTN 40for routing incoming and outgoing voice calls for the enterprise. ThePBX 16 is connected to the PSTN 40 via DID trunks or PRI trunks, forexample. The PBX 16 may use ISDN signaling protocols for setting up andtearing down circuit-switched connections through the PSTN 40 andrelated signaling and communications. In some embodiments, the PBX 16may be connected to one or more conventional analog telephones 19. ThePBX 16 is also connected to the enterprise network 20 and, through it,to telephone terminal devices, such as digital telephone sets 17,softphones operating on computers 15, etc. Within the enterprise, eachindividual may have an associated extension number, sometimes referredto as a PNP (private numbering plan), or direct dial phone number. Callsoutgoing from the PBX 16 to the PSTN 40 or incoming from the PSTN 40 tothe PBX 16 are typically circuit-switched calls. Within the enterprise,e.g. between the PBX 16 and terminal devices, voice calls are oftenpacket-switched calls, for example Voice-over-IP (VoIP) calls.

The enterprise network 20 may further include a Service ManagementPlatform (SMP) 18 for performing some aspects of messaging or sessioncontrol, like call control and advanced call processing features. TheSMP 18 may, in some cases, also perform some media handling.Collectively the SMP 18 and PBX 16 may be referred to as the enterprisecommunications platform, generally designated 14. It will be appreciatedthat the enterprise communications platform 14 and, in particular, theSMP 18, is implemented on one or more servers having suitablecommunications interfaces for connecting to and communicating with thePBX 16 and/or DID/PRI trunks. Although the SMP 18 may be implemented ona stand-alone server, it will be appreciated that it may be implementedinto an existing control agent/server as a logical software component.As will be described below, the SMP 18 may be implemented as amulti-layer platform.

The enterprise communications platform 14 implements the switching toconnect session legs and may provide the conversion between, forexample, a circuit-switched call and a VoIP call, or to connect legs ofother media sessions. In some embodiments, in the context of voice callsthe enterprise communications platform 14 provides a number ofadditional functions including automated attendant, interactive voiceresponse, call forwarding, voice mail, etc. It may also implementcertain usage restrictions on enterprise users, such as blockinginternational calls or 1-900 calls. In many embodiments, SessionInitiation Protocol (SIP) may be used to set-up, manage, and terminatemedia sessions for voice calls. Other protocols may also be employed bythe enterprise communications platform 14, for example, Web Services,Computer Telephony Integration (CTI) protocol, Session InitiationProtocol for Instant Messaging and Presence Leveraging Extensions(SIMPLE), and various custom Application Programming Interfaces (APIs),as will be described in greater detail below.

One of the functions of the enterprise communications platform 14 is toextend the features of enterprise telephony to the mobile devices 11.For example, the enterprise communications platform 14 may allow themobile device 11 to perform functions akin to those normally availableon a standard office telephone, such as the digital telephone set 17 oranalog telephone set 15. Example features may include direct extensiondialing, enterprise voice mail, conferencing, call transfer, call park,etc.

Reference is now made to FIGS. 2 to 4, which show example embodiments ofthe enterprise communications system 14. Again, although references aremade below to “calls” or call-centric features it will be appreciatedthat the architectures and systems depicted and described are applicableto session-based communications in general and, in some instances, tomessaging-based communications.

FIG. 2 illustrates an embodiment intended for use in a circuit-switchedTDM context. The PBX 16 is coupled to the SMP 18 via PRI connection 60or other suitable digital trunk. In some embodiments, the PRI connection60 may include a first PRI connection, a second PRI connection, and achannel service unit (CSU), wherein the CSU is a mechanism forconnecting computing devices to digital mediums in a manner that allowsfor the retiming and regeneration of incoming signals. It will beappreciated that there may be additional or alternative connectionsbetween the PBX 16 and the SMP 18.

In this embodiment, the SMP 18 assumes control over both call processingand the media itself. This architecture may be referred to as “FirstParty Call Control”. Many of the media handling functions normallyimplemented by the PBX 16 are handled by the SMP 18 in thisarchitecture. Incoming calls addressed to any extension or direct dialnumber within the enterprise, for example, are always first routed tothe SMP 18. Thereafter, a call leg is established from the SMP 18 to thecalled party within the enterprise, and the two legs are bridged.Accordingly, the SMP 18 includes a digital trunk interface 62 and adigital signal processing (DSP) conferencing bridge 64. The DSPconferencing bridge 64 performs the bridging of calls for implementationof various call features, such as conferencing, call transfer, etc. Thedigital trunk interface 62 may be implemented as a plurality oftelephonic cards, e.g. Intel Dialogic cards, interconnected by a bus andoperating under the control of a processor. The digital trunk interface62 may also be partly implemented using a processor module such as, forexample, a Host Media Processing (HMP) processor.

The SMP 18 may include various scripts 66 for managing call processing.The scripts 66 are implemented as software modules, routines, functions,etc., stored in non-volatile memory and executed by the processor of theSMP 18. The scripts 66 may implement call flow logic, business logic,user preferences, call service processes, and various featureapplications.

FIG. 3 shows another embodiment in which the PBX 16 performs thefunctions of terminating and/or bridging media streams, but call controlfunctions are largely handled by the SMP 18. In this embodiment, the SMP18 may be referred to as a call control server 18. This architecture maybe referred to as “Third-Party Call Control”.

The call control server 18 is coupled to the PBX 16, for example throughthe LAN, enabling packet-based communications and, more specifically,IP-based communications. In one embodiment, communications between thePBX 16 and the call control server 18 are carried out in accordance withSIP. In other words, the call control server 18 uses SIP-basedcommunications to manage the set up, tear down, and control of mediahandled by the PBX 16. In one example embodiment, the call controlserver 18 may employ a communications protocol conforming to theECMA-269 or ECMA-323 standards for Computer Supported TelecommunicationsApplications (CSTA).

FIG. 4 shows yet another embodiment of the enterprise communicationssystem 14. This embodiment reflects the adaptation of an existing set ofcall processing scripts to an architecture that relies on third-partycall control, with separate call control and media handling. The SMP 18includes a call processing server 74. The call processing server 74includes the scripts or other programming constructs for performing callhandling functions. The SMP 18 also includes a SIP server 72 and a mediaserver 76. The separate SIP server 72 and media server 76 logicallyseparate the call control from media handling. The SIP server 72interacts with the call processing server 74 using acomputer-implemented communications handling protocol, such as one ofthe ECMA-269 or ECMA-323 standards. These standards prescribe XML basedmessaging for implementing Computer Supported TelecommunicationsApplications (CSTA).

The SIP server 72 interacts with the media server 76 using SIP-basedmedia handling commands. For example, the SIP server 72 and media server76 may communicate using Media Server Markup Language (MSML) as definedin IETF document Saleem A., “Media Server Markup Language”, InternetDraft, draft-saleem-msml-07, Aug. 7, 2008. The media server 76 may beconfigured to perform Host Media Processing (HMP).

Other architectures or configurations for the enterprise communicationssystem 14 will be appreciated by those ordinarily skilled in the art.

Reference is now made to FIG. 5, which shows another embodiment of theenterprise communications system 14 with a Third Party Call Controlarchitecture. In this embodiment, the SMP 18 is a multi-layer platformthat includes a protocol layer 34, a services layer 36 and anapplication layer 38. The protocol layer 34 includes a plurality ofinterface protocols configured for enabling operation of correspondingapplications in the application layer 38. The services layer 36 includesa plurality of services that can be leveraged by the interface protocolsto create richer applications. Finally, the application layer 38includes a plurality of applications that are exposed out to thecommunication devices and that leverage corresponding ones of theservices and interface protocols for enabling the applications.

Specifically, the protocol layer 34 preferably includes protocols whichallow media to be controlled separate from data. For example, theprotocol layer 34 can include, among other things, a Session InitiationProtocol or SIP 80, a Web Services protocol 82, an ApplicationProgramming Interface or API 84, a Computer Telephony Integrationprotocol or CTI 86, and a Session Initiation Protocol for InstantMessaging and Presence Leveraging Extensions or SIMPLE protocol 88. Itis contemplated that the interface protocols 80-88 are plug-ins that caninterface directly with corresponding servers in the enterprise network20, which will be further described below.

For the purposes of this disclosure, SIP 80 will be utilized, althoughit is appreciated that the system 10 can operate using the abovedisclosed or additional protocols. As known by those of ordinary skillin the art, SIP is the IETF (Internet Engineering Task Force) standardfor multimedia session management, and more specifically is anapplication-layer control protocol for establishing, maintaining,modifying and terminating multimedia sessions between two or moreendpoints. As further known by those of ordinary skill in the art, theSIP protocol 80 includes two interfaces for signaling: SIP-Trunk(hereinafter referred to as “SIP-T”) and SIP-Line (hereinafter referredto as “SIP-L”). Specifically, the SIP-T interface is utilized when theendpoint is a non-specific entity or not registered (i.e., whencommunicating between two network entities). In contrast, the SIP-Linterface is utilized when the endpoint is registered (i.e., whendialing to a specific extension). The specific operation of the system10 utilizing SIP 80 will be described in further detail below.

The SMP 18 also includes a plurality of enablers, among other things, aVoIP enabler 90, a Fixed Mobile Convergence or FMC enabler 92, aconference services enabler 94, a presence enabler 96 and an InstantMessaging or IM enabler 98. Each of the enablers 90-98 are used bycorresponding services in the services layer 36 that combine one or moreof the enablers. Each of the applications in the application layer 38 isthen combined with one or more of the services to perform the desiredapplication. For example, a phone call service may use the VoIP or PBXenabler, and an emergency response application may use the phone callservice, an Instant Messenger service, a video call service, and emailservice and/or a conference service.

The application layer 38 may include a conference services application63 that, together with the conference services enabler 94, enablesmultiple communication devices (including desk telephones and personalcomputers) to participate in a conference call through use of acentralized conference server 55. As seen in FIG. 5, the conferenceserver 55 is provided in the enterprise network 20 and is incommunication with the conference services enabler 94 preferably throughthe SIP protocol 80, although it is recognized that additional protocolsthat control media separate from data may be appropriate, such as theWeb Services protocol 82 or the CTI protocol 86. As will be described infurther detail below, the conference call server 55 is configured fordirecting media and data streams to and from one or more communicationdevices (i.e., mobile devices 11, telephones 17, and computers 15).

Turning now to FIGS. 6A through 7B, the general operation of the system10 using SIP 80 as the signaling protocol will be discussed, although itis recognized that the present system is not limited to the processesdiscussed herein. The signaling descriptions that follow are based onThird Party Call Control architecture, such as that illustrated in FIG.3 or 5. It will be appreciated that similar but slightly modifiedsignaling may be used in a First Party Call Control architecture,wherein the PBX 16 will pass media through to the SMP 18 for directmedia handling by the SMP 18. Variations in the signaling to adapt tovarious architectures will be appreciated by those ordinarily skilled inthe art.

FIG. 6A provides a signaling diagram for a call originating from one ofthe mobile devices 11 to a target phone 101 connected to a PrivateBranch Exchange Server or PBX 16 provided within the enterprise network20. First, the device 11 sends a mobile originated call request with itscellular number and the destination number of the target phone 101 tothe SMP 18 (block 100). In some embodiments, the mobile originated callrequest may be sent via the WLAN through the enterprise server 12. Inanother embodiment, the call request may be sent via the PLMN/PSTNthrough the PBX 16, for example as an SMS message or using anothermessaging operation. The SMP 18 confirms the call request by sending theDNIS number to the device 11 (block 102). Next, the device 11 makes acellular call using the DNIS number, which is received by the PBX 16(block 104). As the DNIS has been configured in the PBX 16 to be routedto the SMP 18 via SIP-T, in response to the incoming call, the PBX 16sends an invite over SIP-T with the DNIS number to the SMP 18 (block106). The SMP 18 matches the incoming call with the expected call fromthe mobile, and if correct, acknowledges the invite by sending a 200 OKsignal to the PBX 16, indicating that the mobile call leg is established(block 108).

The SMP 18 then sets up the outgoing call leg to the destination. Itdoes this by sending an invite over SIP-L to the PBX 16 with thedestination number of the target phone (block 110). SIP-L is used sothat the call can be correctly attributed to the individual within theorganization within any call records that are being maintained by thePBX 16. When the invite is received, the PBX 16 dials the destinationnumber to the target phone 101 (block 112), and the target phone 101answers the call (block 114). When the target phone 101 is answered, thePBX 16 sends a 200 OK signal to the SMP 18 indicating that the targetphone 101 is ready to receive data (block 115). The SMP 18 then sends aninvite over SIP-T to the PBX 16 and shuffles the SDP (SessionDescription Protocol, as known to those of ordinary skill in the art) toconnect the call legs (block 116). When the call legs are connected, thePBX 16 sends a second 200 OK signal to the SMP 18 (block 118), and theusers of the device 11 and target phone 101 can communicate with eachother.

Note that between the cellular call leg being established and theoutgoing call leg being answered, the mobile user hears ringing tones.These ringing tones may be provided by the PBX 16 using the presentationof early media from the outgoing call leg, or they may be generatedlocally on the device 11 if early media is not available. In the lattercase, it will be necessary to localize the ringing tone to match thetone normally heard with a call through the PBX 16.

The above description is known as a “mobile initiated” call, because theSMP 18 provides the mobile device 11 with the DNIS number into which themobile device 11 has called. Alternatively, the mobile originated callcould be “PBX initiated”, as shown in FIG. 6B. Specifically, in aPBX-initiated call, upon receipt of the mobile originated call request(block 120), the SMP 18 confirms receipt of the call to the mobiledevice 11 with an ANI number (block 122), which the mobile device usesto identify the incoming call from the PBX 16. The PBX 16 then sends aninvite over SIP-T to the PBX 16 with the cellular number of the deviceand the ANI number that is attached to the outgoing call (block 124).Upon receipt of the invite, the PBX 16 makes a cellular call to thedevice 11 (block 126), which is answered by the device (block 128). Thedevice 11 checks the ANI number in the incoming call to confirm if thenumber is actually from the PBX 16. If the ANI number is stripped forany particular reason, then the device 11 may be configured to answerthe call as a regular cellular call, or it may reject the call asunknown. When the device 11 answers the PBX-initiated call, the PBX 16sends a 200 OK signal to the SMP 18, indicating that the call leg to thedevice is established (block 130).

In response, the SMP 18 sends an invite over SIP-L with the destinationnumber of the target phone 101 to the PBX 16 (block 132). When theinvite is received at the PBX 16, the PBX dials the destination numberto the target phone 101 (block 134), the target phone 101 picks up thecall (block 136), and a 200 OK signal is sent from the PBX 16 to the SMP18 (block 138), indicating that the target phone 101 is also ready toreceive data. In response to the 200 OK, the SMP 18 sends an invite tothe PBX 16, shuffling the SDP to connect the call legs (block 140).Finally, when the call legs are connected, the PBX 16 sends a second 200OK signal to the SMP 18, and the users of the device 11 and target phone101 are able to communicate with each other.

In both instances, the SMP 18 is performing third party call control ofthe two call legs, the PBX 16 remaining in control of the call. Thedecision of whether to proceed with a mobile-initiated call or aPBX-initiated call can be set by policy. Specifically, the option toselect either mobile-initiated or PBX-initiated calls is a featureprovided in the SMP 18, and an administrator for the enterprise network20 can determine which setting to use. For example, in some cases it maybe more cost effective for the corporation to utilize PBX-initiatedcalls rather than mobile-initiated calls, and vice versa. However, it isappreciated that the system 10 is not limited to the above processes.

FIGS. 7A and 7B are signaling diagrams illustrating a mobile terminatedcall utilizing SIP 80. Specifically, and for the purposes of thisdisclosure, the target phone 101 is originating the call, which willsend a call to the mobile device. Turning first to FIG. 7A, an incomingcall is made from the target phone 101 to the PBX 16 (block 150). Whenthe call is received at the PBX 16, the PBX 16 sends an invite to theSMP 18 over SIP-L (block 152).

In response to the invite, the SMP 18 sends a call request with the DNISnumber and source details to the device 11 (block 154), which isconfirmed to the SMP (block 156). In addition to confirming the call,the mobile device 11 sends a cellular call to the DNIS number at the PBX16 (block 158). Again, as the DNIS number is routed in the dialing plansto the SMP 18, upon receipt of the cellular call, the PBX 16 sends aninvite over SIP-T to the SMP 18 with the DNIS number (block 160). Inresponse to the invite, a “200 OK” signal is sent over SIP-T from theSMP 18 to the PBX 16, acknowledging that the call leg to the mobiledevice 11 is established (block 162). Finally, the initial invite (block152) is acknowledged with the “200 OK” signal with the cellular SDP, atwhich point the call legs are joined and the target phone 101 and device11 can communicate with each other on the call.

The diagram shown in FIG. 7A illustrates a “mobile-initiated” call,because, as discussed above with respect to FIGS. 6A and 6B, the SMP 18presents the mobile device 11 with the DNIS number at the PBX 16 intowhich to call. However, it is also possible to employ a “PBX-initiated”mobile terminated call, as shown in FIG. 7B, where the PBX 16 sends anincoming call to the device 11 with the ANI number of the target phone101.

Specifically, similar to the mobile initiated call described above andshown in FIG. 7A, the target phone 101 sends an incoming call to thedestination number of the device, which is received at the PBX 16 (block170). Upon receipt of the call, the PBX 16 sends an invite over SIP-L tothe SMP 18 (block 172) with the source number of the target phone 101.In response to the invite, the SMP 18 sends a call request with thesource number to the device 11 (block 174), with the ANI number thedevice should expect in the incoming call, the call request beingconfirmed by the device (block 176). At this point in the PBX-initiatedcall, the SMP 18 sends an invite over SIP-T to the PBX 16 with thecellular number and ANI number to use (block 178), prompting the PBX 16to make a cellular call to the device 11 with the ANI number (block180), prompting the device to ring. The device 11 answers the call(block 182), and a “200 OK” signal is sent from the PBX 16 to the SMP18, acknowledging that the cellular call leg to the device 11 isestablished (block 184). In response, a “200 OK” signal is also sentfrom the SMP 18 to the PBX 16, acknowledging that the call leg to thetarget phone 101 is also established (block 186). The SMP 18 shufflesthe SDP to connect the call legs, the call legs are joined, and thetarget phone 101 and device 11 can communicate with each other on thecall.

As discussed above with respect to FIGS. 6A and 6B, the SMP 18 remainsin control of the signaling between the target phone 101 and the mobiledevice 11 in both the mobile-initiated and PBX-initiated calls. Again,the decision to proceed with a mobile-initiated call or a PBX-initiatedcall is based on policy and may be set by a system administrator. Insome cases, it may be more efficient or cost effective for theadministrator to decide that PBX-initiated calls should be used, and inother cases, it may be more efficient or cost effective formobile-initiated calls to be utilized. As these policy decisions mayvary by organization and are not imperative to the scope of the presentapplication, they will not be discussed in further detail.

FIG. 1B presents an alternate view of the system of FIG. 1A showingthree types of data flow: cellular voice data, cellular data and IPdata, between selected components of system 10. Generally, the voicechannel carries voice call data and may therefore accordingly beoptimized for voice data, whereas the data channel carries computerdata. Mobile devices 11 may send and receive data over PLMN 50 via thecellular data channel and/or the data channel. Relay 26, enterpriseserver 12 and enterprise communications platform 14 also may send andreceive computer data, e.g. from mobile device 11 over the data channel(via PLMN 50). As explained previously, voice calls may be carried inthe form of IP data (VoIP) over the cellular data channel and/or withinthe enterprise network 20. Cellular voice data incoming from PLMN 50 tothe enterprise may be converted into IP data by a call manager 21 suchas a Cisco Unified Communications Manager. Call manager 21 may convertcellular voice data into corresponding IP data for sending to one ormore digital telephone sets 17. Furthermore, cellular data coming intothe enterprise via the relay 26—enterprise server 12—enterprisecommunications platform 14 route may be sent to one or more digitaltelephone sets 17 as IP data. In the exemplary embodiment, enterprisecommunications platform 14 is generally described as the server tomobile devices 11. Therefore, in the following disclosure, enterprisecommunications platform 14 may be generally referred to as server 14.

As explained previously, with reference to FIG. 1A, the enterprisecommunications platform 14 may provide mobile voice services to mobiledevices 11 so as to allow a given mobile device 11 to act in the samemanner as a PBX/IP-PBX 16—connected desk phone (e.g. telephone set 17).Specifically, the enterprise communications platform 14 may provide asuite of call setup features and in-call features much like the featuresavailable to a PBX/IP-PBX 16—connected desk phone. These features may beimplemented in a message exchange protocol between mobile devices 11 andserver 14. Specifically, and as will be more fully explained below, auser-originated request for a particular feature may initiate a messageexchange sequence between the user's mobile device 11 and the server 14.These messages may be encoded by modulating a signal in accordance witha data modulation technique, as will be understood by those of ordinaryskill in the art. The resulting data signal may then be transmitted bythe mobile device 11 to the server 14, and vice versa via PSTN 40, PLMN50 or WAN 30 or a combination thereof.

In an exemplary embodiment of system 10, dual-tone multi-frequency(DTMF) signaling is used in the exemplary message exchange protocol formessage exchange between mobile devices 11 and server 14. As may beappreciated by a person of ordinary skill in the art, DTMF signalingoperates as follows: each symbol in the set {0-9, *, #, A-D} is laid outin a 4-by-4 matrix, and a particular frequency associated with eachsymbol in the set. The DTMF matrix is provided below:

1209 Hz 1336 Hz 1477 Hz 1633 Hz 697 Hz 1 2 3 A 770 Hz 4 5 6 B 852 Hz 7 89 C 941 Hz * 0 # D

Specifically, each symbol in the DTMF symbol set is represented by acombination of two frequencies. For example, to represent the symbol“1”, a 697 Hz sinusoidal wave is combined with a 1209 Hz sinusoidalwave. The resulting combined wave may be audible as a “DTMF tone”. Totransmit the symbol “1”, the combined wave, or “DTMF tone” associatedwith the symbol “1” may be transmitted to the intended recipient overthe voice channel. The recipient may then decode the received wave, or“DTMF tone” to determine which symbol was sent. In this disclosure, theterms “DTMF symbol” and “DTMF tone” may be used interchangeably.However, in certain contexts the term “DTMF symbol” may be used tospecifically refer to one of DTMF symbols {0-9, *, #, A-D}, and the term“DTMF tone” to refer to the audible representation of a particular DTMFsymbol.

The universe of messages in the exemplary exchange protocol may bestored in two tables. The first table may be a device-to-server messagetable storing the universe of messages sent by a mobile device 11 toserver 14, i.e. possible messages mobile device 11 could send to server14. The second table may be a server-to-device message table storing theuniverse of message sent by server 14 to mobile devices 11, i.e.possible messages server 14 could send to device 11.

Table 900 (FIG. 8), an exemplary device-to-server message table,contains an exemplary list of sixteen possible in-call feature controlmessages that may be sent from a mobile device 11 to the server 14during an active voice call. Table 900 may be stored in a memory (notshown) of server 14. Each of rows 902, 904, 906, 908, 910, 912, 914,916, 918, 920, 922, 924, 926, 928, 930 and 932 lists an exemplarymapping of control messages to DTMF sequences. For example, row 905specifies that the HOLD_CALL control message is mapped to the DTMFsequence “C3C”. The HOLD_CALL message, may, for example, indicate that auser wishes to put an active voice call on hold. To send a HOLD_CALLmessage to server 14, mobile device 11 may send a sequence of three DTMFtones (“DTMF tone sequence”), each associated with the DTMF symbols “C”,“3” and “C” respectively, to server 14 in a conventional manner. Uponreceipt, server 14 may decode the received DTMF tone sequence, in aconventional manner, to determine that the symbols “C”, “3” and “C” weresent by the mobile device 11. Further, server 14 may identify that thesymbol sequence “C3C” is mapped to the HOLD_CALL message, and maythereby determine that that particular mobile device 11 (or moreaccurately, the user of that particular mobile device 11) is requestingthat the active voice call be put on hold. Server 14 may then takefurther action as appropriate.

Table 1000 (FIG. 9), an exemplary server-to-device message table,contains an exemplary list of nineteen possible in-call feature controlmessages that may be sent from server 14 to a mobile device 11 during anactive voice call. Table 1000 may be stored in a memory (not shown) ofmobile device 11. Each of rows 1002, 1004, 1006, 1008, 1010, 1012, 1014,1016, 1018, 1020, 1022, 1024, 1026, 1028, 1030, 1032, 1034 and 1036specifies an exemplary mapping of control messages to DTMF sequences.For example, as specified in row 1002, the TARGET_RINGING controlmessage is mapped to the DTMF sequence “*C”. This message may indicate,for example, that the called party device is ringing. To send theTARGET_RINGING message to a mobile device 11, server 14 may send the “*”tone followed by the “C” tone to the mobile device 11 in sequence in aconventional manner. Upon receipt, the mobile device 11 may decode thereceived DTMF tone sequence, in a conventional manner, to determine thatthe symbols “*” and “C” were sent by server 14. Mobile device 11 mayfurther identify that the symbol sequence “*C” is mapped to theTARGET_RINGING message, and may take further action as appropriate.

Moreover, an indicator may be kept in server-to-device message table1000 indicating that receipt of a particular message should beacknowledged. In particular, a value of “1” in the column entitled “ACK”for a particular message may indicate that receipt of that particularmessage should be acknowledged. Thus, the value of “1” in the ACK columnof row 1006 indicates that receipt of a TARGET_ANSWERED message bymobile device 11 should be acknowledged (by sending DTMF tone “D” (FIG.10) to server 14, as further described below). Conversely, the values of“0” in the ACK column for all other rows of table 1000 indicates thatreceipt of any one of the other messages need not be acknowledged bymobile device 11.

Table 1100 (FIG. 10) lists two special non-control messages that may besent by a mobile device 11 to server 14. Table 1100 may be stored in thememory of mobile device 11. Specifically, table 1100 specifies that anACK (“acknowledge”) message is mapped to a single DTMF tone, “D”, and aNACK (“negative acknowledgement”) message is mapped to a single DTMFtone, “B”. The functions of the ACK and NACK messages will becomeapparent below.

It may be noted that each exemplary control message in tables 900 and1000 consists of a sequence of two to four DTMF tones. The mapping ofeach control message in the universe of all control messages to aparticular sequence of DTMF tones may of course be arbitrary. However,as will become apparent, strategic mapping of particular sequences ofDTMF tones to particular control messages, and strategic selection ofparticular DTMF tones in certain sequences, may be advantageous.Notably, such strategic mapping may increase the reliability of DTMFsignaling between mobile devices 11 and voice mobile server 18 in system10, as detailed below.

DTMF has traditionally been regarded as an unreliable data transmissionmechanism. For example, DTMF tones can be lost or corrupted intransmission. DTMF tone detectors may sometimes detect false DTMF tones.Additionally, it takes approximately 100 ms to send a single DTMF tone,therefore DTMF is a relatively slow method of communication.

Moreover, the design of enterprise communications platform 14 furtheradds to the challenges of using DTMF signaling in system 10. Forexample, enterprise communications platform 14 is a real-time system andthus requires virtually instant communication between server 14 and amobile device 11. Thus, keeping the number of DTMF tones sent permessage to as few as possible, and limiting the number of instances ofre-transmission of messages, may be desirable (because, for example,long transmission times may result in user perception of sluggish systemresponse times). Second, since DTMF tones are transmitted over the voicechannel in the exemplary embodiment and are within human-audible range,a multitude of DTMF tones may degrade user experience since a user wouldhear these tones in his or her mobile device earpiece. Thus, for thisreason also, it may be desirable to reduce the number of DTMF tonesexchanged between the mobile device 11 and server 14.

Accordingly, a method for increasing reliability of DTMF signalingbetween mobile device 11 and server 14 is provided, which method mayminimize signaling. In overview, the method includes mapping certaincontrol messages to DTMF tone sequences such that even if only a part ofa complete DTMF tone sequence is received, e.g., due to transmissionerror or decoding errors, the recipient mobile device 11 maynevertheless identify the intended message. The method may furtherinclude repeated transmission by server 14 of certain very importantcontrol messages until receipt is acknowledged by an intended recipientmobile device 11. The method may further include transmission of a“negative acknowledgement” message by mobile device 11 to server 14 uponreceipt of a DTMF tone sequence that it cannot identify as a recognizedmessage.

More specifically, the exemplary embodiment includes redundantly codingcertain messages so that an error correction algorithm can be applied toa received sequence of tones to recover the sequence of tones that wereactually sent. For example, the CALL_DISCONNECTED (row 1036) andSECOND_CALL_DISCONNECTED (row 1038) messages listed in table 1000 (FIG.9) map to DTMF sequences “88C” and “99C”, respectively. Notably, noother control message that may be sent by server 14 to mobile device 11,as specified in table 1000, maps to “88C” and “99C”, or maps to any twosequence sub-sequence of “88C” and “99C”. Further, the only singlesignal that does not uniquely map to “88C” or “99C” is the signal “C”.Thus, conveniently, even if mobile device 11 does not receive thecomplete sequence of tones “88C” but only receives a sub-sequence ofthose tones, e.g. “8”, “88”, “8C”, it may be able to identify thereceived tones as the CALL_DISCONNECTED message. Similarly, if mobiledevice 11 receives a sub-sequence of the tones “99C”, it may be able toidentify the received tones as the SECOND_CALL_DISCONNECTED message.

As will be noted from tables 900 and 1000, not all messages areredundantly coded. In these instances, contextual error correction maybe performed. For example, the CALL_HELD_FAILED (table 1000, row 1020)is not redundantly coded. That is, if a mobile device 11 were to receivethe sequence of tones “2C”, it would not necessarily be able to uniquelyidentify a message because the DTMF tones “2C” is a sub-sequence of DTMFtone sequences for several other messages, namely, CALL_FAILED (row1008); TARGET_NOT_FOUND (row 1010); TARGET_NOT_AVAILABLE (row 1012);CALL_RESUME_FAILED (row 1024); and ATTND_TRANSFER_SUCCESS (row 1028).However, in this scenario, mobile device 11 may still be able to deducewhat sequence of tones was actually sent by server 14 by comparing thereceived sequence of tones to messages currently expected by mobiledevice 11. For example, if mobile device 11 had previously sent aHOLD_CALL control message (table 900, row 902) to server 14, it mayexpect to receive in reply a CALL_HELD or CALL_HELD_FAILED message. Uponsending a particular control message to server 14, it may be determinedif server 14 may be expected to reply to that message with a replymessage. If so, device 11 may store a table of expected reply messagesfor a pre-determined time (e.g. 10 minutes—but of course other timeperiods could be used).

Referring to table 1000 (FIG. 9), the CALL_HELD message is mapped to theDTMF sequence “31C” and the CALL_HELD_FAILED message is mapped to theDTMF sequence “32C”. Therefore, since the received sequence of tonesdetected by mobile device 11, “2C”, is a sub-sequence of the sequence“32C” but not of the sequence “31C”, it may be deduced that voice mobileserver 18 actually sent the sequence “32C”, thus identifying that voicemobile server 18 sent a CALL_HELD_FAILED message.

For some features, it may be desired that receipt of control messagesassociated with those features be assured. The TARGET_ANSWERED message(FIG. 9, table 1000, row 1006) is an example of such a message. Thismessage may be sent by server 14 to mobile device 11 to indicate thatthe called party (i.e. the “target”) is connected. In particular, voicemobility server 11 may be designed to refrain from sending any voicedata signals originating from the called party until the calling party,i.e. mobile device 11, acknowledges receipt of the TARGET_ANSWEREDmessage. Absent this requirement, it is possible that the initial partof the called party's conversation could be dropped because mobiledevice 11 is not, for example, in a proper state to receive.Consequently, and in accordance with the exemplary embodiment of thepresent disclosure, receipt of a TARGET_ANSWERED message should beacknowledged by the recipient (i.e., mobile device 11).

Moreover, because the TARGET_ANSWERED message is mapped to a single DTMFtone (i.e. “B”), in the event that the tone is dropped duringtransmission, the intended recipient mobile device 11 may have no way ofknowing that server 14 had sent a message. Even further, in the eventthe tone is corrupted in transmission but nevertheless received bymobile device 11 (e.g. as DTMF tone “C”, rather than tone “B”) mobiledevice 11 may not be able to deduce which message was actually sent.Thus, a mechanism for ensuring proper receipt of the message isrequired. The ACK message may be a suitable mechanism. In exemplarytable 1100 (FIG. 10), row 1102 specifies that the ACK message is mappedto DTMF sequence “D”. Therefore, to send an ACK message, mobile device11 may send the “D” DTMF tone to server 14.

In some cases, mobile device 11 may be unable to identify any recognizedmessages from a sequence of received DTMF tones, due to for example,errors or corruption of the DTMF tones in transmission. For example, ifthe “1” tone in the sequence “1C” (mapping to the TARGET_ALERTINGmessage (Table 1000, row 1004)) was dropped in transmission from server14 to mobile device 11, mobile device 11 may only receive the “C” tone.However, the “C” tone is a part of many other possible server to devicemessages (e.g. CALL_FAILED “22C” (row 1008), TARGET_NOT_FOUND “21C” (row1010)). Thus, mobile device 11 may have no way (in the event the errorcorrection mechanisms previously described fail to identify a message)of ascertaining what sequence of tones server 14 actually transmitted.In such instances, mobile device 11 may send a NACK (“negativeacknowledgement”) message to server 14. In exemplary table 1100 (FIG.10), row 1104 specifies that the NACK message is mapped to DTMF sequence“B”. Therefore, to send a NACK message, mobile device 11 may send the“B” DTMF tone to server 14.

In operation, and with reference to flow diagram S1200 (FIG. 11), uponreceipt of a sequence of one or more DTMF tones, mobile communicationsdevice 11 may decode the sequence of tones using for example, aconventional DTMF signal decoder component of mobile device 11 (notillustrated) (S1202). Mobile device may determine whether the sequenceof tones encode a message (S1204) by, for example, comparing the tonesto tones listed in server-to-device message table 1000 (FIG. 9). Table1000 may be stored in a memory of mobile device 11, as previouslydescribed.

If it is determined that the sequence of tones identify a message (the“identified message”), (i.e. the sequence of tones match a sequence oftones mapped to a particular message listed in server-to-device messagetable 1000), communications device 11 may subsequently determine if theidentified message requires acknowledgement (S1212) by, for example,determining if the “ACK” indicator for the identified message has beenset to “1” in table 1000. If the identified message requiresacknowledgement, mobile device 11 may send an “ACK” message to server14, in the manner previously described (S1214).

However, if no message is identified at S1204, mobile device 11 mayattempt to identify a probable message (S1206) using an error correctionmechanism, further described in conjunction with FIG. 12 below. If,following application of the error correction mechanism, no message isidentified (S1208), mobile device may indicate an error by, for example,sending a “NACK” message to server 14 (S1210), in the manner previouslydescribed. If, following application of the error correction mechanism,a message is identified (S1208), mobile device may subsequentlydetermine if the identified message requires acknowledgement, and if itdoes, acknowledge the message (S1212, S1214).

Operation of the error correction mechanism (S1206) will now bedescribed in conjunction with FIG. 12. To identify a candidate message,mobile device 11 may determine if the received tones map uniquely to amessage (i.e. if the received tones are a sub-sequence of tones mappingto a redundantly coded message, in the manner previously described)(S1206 a). If it does, then the received tones may be identified as thecandidate message (S1206 d), and further operation of mobile device 11may proceed on the assumption that the message actually sent by server14 was the candidate message.

If the received tones do not map uniquely to any messages (i.e. if thereceived tones are a sub-sequence of more than one message), mobiledevice 11 may determine if it is expecting any particular reply messagesfrom server 14. To do so mobile device 11 may examine messages stored inthe expected reply message table (S1206 b). If one or more candidatereply messages are currently expected (i.e. there is at least onemessage stored in the expected reply message table), mobile device 11may determine if the received DTMF sequence maps uniquely to one of thecandidate reply messages (S1206 c), in the manner previously described.If it does, then mobile device 11 may identify the received tones as thecandidate message (S1206 d). Subsequent operation of mobile device 11may proceed on the assumption that the message actually sent by server14 was the candidate message. However, if the received tones do notuniquely map to any expected reply messages, mobile device 11 may beunable to identify the message (S1206 e). Similarly, if the receivedtones do not map uniquely to any messages, and no reply messages arecurrently expected from server 14 (S1206 b), then mobile device 11 maybe unable to identify any message (S1206 e) (i.e. may be unable to mapthe received tone sequence to any messages).

Operation of the exemplary embodiment from the server 14 perspectivewill now be described in conjunction with FIGS. 13A-C.

Flow diagram 1400 (FIG. 13A) depicts the simplest case in which server14 sends a redundantly coded message (e.g. CALL_DISCONNECTED (FIG. 9,row 1034) or SECOND_CALL_DISCONNECTED (FIG. 9, row 1036)) to mobiledevice 11 (S1402). Receipt of the message by mobile device 11 may beassumed. Moreover, even if a transmission error occurs resulting inmobile device 11 receiving only a sub-sequence of the tones sent byserver 14, conveniently, mobile device 11 may still identify theintended message in the manner previously discussed.

Flow diagram 1406 (FIG. 13B) depicts operation of server 14 upon receiptof a NACK message (FIG. 10, row 1104) from a mobile device 11 which itserves. Upon receipt of a NACK message (S1410), server 14 may determineif it sent a message to the mobile device 11 which sent the NACK messagein a past window of time (S1412) (e.g. past 1 minute—of course, windowsof time other than 1 minute could be employed): If it has, server 14 mayresend the message (S1414) (because, for example, the DTMF tones mayhave been corrupted in transmission in such a way that mobile device 11was unable to identify a candidate message in the manner previouslydescribed).

Flow diagram 1416 (FIG. 13C) depicts operation of server 14 to send aserver message to mobile device 11 that requires an acknowledgement ofreceipt, such as exemplary TARGET_ANSWERED message (FIG. 9, row 1006).Specifically, server 14 may send the TARGET_ANSWERED message to mobiledevice (S1418). It may subsequently check whether it has received an ACKmessage (FIG. 10 row 1102) from mobile device 11 (S1420). If an ACKmessage is received from mobile device 11, acknowledging receipt of theTARGET_ANSWERED message, operation may end. However, if no ACK messagehas been received, server 14 may re-send the TARGET_ANSWERED messageuntil it receives an ACK from mobile device 11.

Exemplary interactions between server 14 and a mobile device 11, inaccordance with the present disclosure are provided in FIGS. 14 and 15.Specifically, FIG. 14 is a signal diagram showing a call request frommobile device 11 to server 14 (block 1500). The call request may be ofthe form described in FIG. 6A and may, in particular, include thetelephone number of the target (i.e. called) party (not shown). Server14 (specifically, SMP 18 in conjunction with PBX 16—FIG. 6A/6B) may setup the connection with the target party in the manner previouslydescribed. Upon receiving an indication that the called party hasanswered (e.g. Target Phone Answers block 114 or Answers block 136—FIG.6A/6B), server 14 may send a TARGET_ANSWERED message to mobile device 11(block 1502). Mobile device 11 may determine that the TARGET_ANSWEREDmessage must be acknowledged, and may, accordingly, send an ACK messageback to server 14 (block 1504).

When mobile device 11 receives an unknown message (FIG. 15, block 1600),it may send a NACK message to server 14 (block 1602), thus promptingserver 14 to check whether it had sent a message to mobile device 11 ina past window of time, and to re-send the message, if required.

Thus, as may now be appreciated, by implementing a message exchangeprotocol between server 14 and mobile devices 11 using DTMF signalingover the voice channel, server 14 and mobile devices 11 may communicateeven when the data channel is unavailable. To account for the fact thatDTMF signaling over the voice channel can be unreliable, “acknowledge”and “negative acknowledgement” mechanisms have been introduced intosystem 10. Additionally, error correction algorithms, such as thecontextual error correction and redundant coding, may be used to correctsome transmission errors, thereby reducing the number of instancesrequiring re-transmission of messages.

While not described in detail, it will be understood that the disclosedmethods, exemplary message exchange protocol and components thereof(e.g. the message tables) may be implemented in software usingprogramming languages such as JAVA, C++, etc., or in a combination ofhardware and software. More specifically, computer readable medium 13and computer readable medium 41 may store executable instructions whichwhen executed by a processor (not shown) of mobile device 11 or server14, respectively, cause mobile device 11 and server 14 to perform thedisclosed methods.

Furthermore, it may be understood that message tables 900, 1000 and 1100need not necessarily be stored as separate tables, nor in the locationsdescribed above. For example, in an another embodiment, message tables900, 1000 and 1100 may be combined into one table and stored in alocation accessible to server 14 and mobile devices 14 over one or acombination of PSTN 40, WAN 30 and PLMN 50. Moreover, the messagetable(s) may be stored in the form of a flat file, or in a conventionaldatabase which may be queried by server 14 and mobile devices 14.

Even further, redundant codes may be selected so that application ofcertain conventional error correction algorithms known to those ofordinary skill in the art may be applied.

Certain other adaptations and modifications of the described embodimentscan be made. Therefore, the above discussed embodiments are consideredto be illustrative and not restrictive.

What is claimed is:
 1. At a mobile communications device server, amethod of communicating with a mobile communications device served bysaid server, said method comprising: upon receipt of an indicatorindicating receipt by said mobile communications device of anunrecognized message: determining if a first message was sent to saidmobile communications device in a previous pre-determined window oftime; and re-sending said first message if said determining determinesthat said first message was sent to said mobile communications device insaid previous pre-determined window of time; sending a second message tosaid mobile communications device, said second message encoded by aparticular unique sequence of DTMF tones wherein no sub-sequence of saidparticular unique sequence matches sequences or sub-sequences of tonesencoding any other possible message such that said mobile communicationsdevice is able to identify said second message even if only asub-sequence of said particular unique sequence is received; and sendinga third message to said mobile communications device, said third messageencoded by a further particular sequence of DTMF tones wherein one ormore sub-sequences of said further articular unique sequence matchessequences or sub-sequences of tones encoding at least one other possiblemessage but said third message is only sent after a sub-set of earliermessages such that said mobile communications device is able to identifysaid third message in context of earlier messages received.
 2. Themethod of claim 1 further comprising: repeatedly sending a secondfurther message until an indicator indicating receipt of said furthermessage by said mobile communications device is received by said server,said indicator comprising a sequence of at least one DTMF tone.
 3. Themethod of claim 2 wherein said further message is encoded by a sequenceof at least one DTMF tone and wherein said indicator comprising asequence of at least one DTMF tone is mapped to an acknowledge message.4. The method of claim 1 wherein said receipt of an indicator indicatingreceipt by said mobile communications device of an unrecognized messagecomprises receiving a DTMF tone mapped to a negative acknowledgementmessage.
 5. A mobile communications device server operable to executethe method of claim
 1. 6. A computer-readable medium comprising computerexecutable instructions which when executed by a processor of a mobilecommunications device server cause said server to execute the method ofclaim
 1. 7. At a mobile communications device server, a method ofcommunicating with a mobile communications device served by said server,said method comprising: sending a first message to said mobilecommunications device, said first message encoded by a first particularunique sequence of DTMF tones wherein no sub-sequence of said firstparticular unique sequence matches sequences or sub-sequences of tonesencoding any other possible message such that said mobile communicationsdevice is able to identify said first message even if only asub-sequence of said first particular unique sequence is received; andsending a second message to said mobile communications device, saidsecond message encoded by a second particular sequence of DTMF toneswherein one or more sub-sequences of said second particular uniquesequence matches sequences or sub-sequences of tones encoding at leastone other possible message but said second message is only sent after asub-set of earlier messages such that said mobile communications deviceis able to identify said second message in context of earlier messagesreceived.
 8. The method of claim 7 further comprising: upon receipt ofan indicator indicating receipt by said mobile communications device ofan unrecognized message: determining if a given message was sent to saidmobile communications device in a previous pre-determined window oftime; and re-sending said given message if said determining determinesthat said given message was sent to said mobile communications device insaid previous pre-determined window of time.
 9. The method of claim 8further comprising: repeatedly sending a third message until anindicator indicating receipt of said third message by said mobilecommunications device is received by said server, said indicatorcomprising a sequence of at least one DTMF tone.
 10. The method of claim9 wherein said third message is encoded by a sequence of at least oneDTMF tone and wherein said indicator comprising a sequence of at leastone DTMF tone is mapped to an acknowledge message.
 11. The method ofclaim 9 wherein said receipt of an indicator indicating receipt by saidmobile communications device of an unrecognized message comprisesreceiving a DTMF tone mapped to a negative acknowledgement message. 12.A mobile communications device server operable to execute the method ofclaim
 7. 13. A computer-readable medium comprising computer executableinstructions which when executed by a processor of a mobilecommunications device server cause said server to execute the method ofclaim 7.